Showing papers by "Indian Institute of Science published in 2006"

Increasing Trend of Extreme Rain Events Over India in a Warming Environment

Abstract: Against a backdrop of rising global surface temperature, the stability of the Indian monsoon rainfall over the past century has been a puzzle By using a daily rainfall data set, we show (i) significant rising trends in the frequency and the magnitude of extreme rain events and (ii) a significant decreasing trend in the frequency of moderate events over central India during the monsoon seasons from 1951 to 2000 The seasonal mean rainfall does not show a significant trend, because the contribution from increasing heavy events is offset by decreasing moderate events A substantial increase in hazards related to heavy rain is expected over central India in the future

Ever-fluctuating single enzyme molecules: Michaelis-Menten equation revisited

Abstract: Enzymes are biological catalysts vital to life processes and have attracted century-long investigation. The classic Michaelis-Menten mechanism provides a highly satisfactory description of catalytic activities for large ensembles of enzyme molecules. Here we tested the Michaelis-Menten equation at the single-molecule level. We monitored long time traces of enzymatic turnovers for individual b-galactosidase molecules by detecting one fluorescent product at a time. A molecular memory phenomenon arises at high substrate concentrations, characterized by clusters of turnover events separated by periods of low activity. Such memory lasts for decades of timescales ranging from milliseconds to seconds owing to the presence of interconverting conformers with broadly distributed lifetimes. We proved that the Michaelis-Menten equation still holds even for a fluctuating single enzyme, but bears a different microscopic interpretation.

The ubiquitin-proteasome system.

Abstract: The 2004 Nobel Prize in chemistry for the discovery of protein ubiquitination has led to the recognition of cellular proteolysis as a central area of research in biology. Eukaryotic proteins targeted for degradation by this pathway are first ‘tagged’ by multimers of a protein known as ubiquitin and are later proteolyzed by a giant enzyme known as the proteasome. This article recounts the key observations that led to the discovery of ubiquitin-proteasome system (UPS). In addition, different aspects of proteasome biology are highlighted. Finally, some key roles of the UPS in different areas of biology and the use of inhibitors of this pathway as possible drug targets are discussed.

A physical mechanism for North Atlantic SST influence on the Indian summer monsoon

Abstract: A link between the Atlantic Multidecadal Oscillation (AMO) and multidecadal variability of the Indian summer monsoon rainfall is unraveled and a long sought physical mechanism linking Atlantic climate and monsoon has been identified. The AMO produces persistent weakening (strengthening) of the meridional gradient of tropospheric temperature (TT) by setting up negative (positive) TT anomaly over Eurasia during northern late summer/autumn resulting in early (late) withdrawal of the south west monsoon and persistent decrease (increase) of seasonal monsoon rainfall. On inter-annual time scales, strong North Atlantic Oscillation (NAO) or North Annular mode (NAM) influences the monsoon by producing similar TT anomaly over Eurasia. The AMO achieves the interdecadal modulation of the monsoon by modulating the frequency of occurrence of strong NAO/NAM events. This mechanism also provides a basis for explaining the observed teleconnection between North Atlantic temperature and the Asian monsoon in paleoclimatic proxies. Citation: Goswami, B. N., M. S. Madhusoodanan, C. P. Neema, and D. Sengupta (2006), A physical mechanism for North Atlantic SST influence on the Indian summer monsoon

Temperature dependence of the resistance of metallic nanowires of diameter≥15nm: applicability of Bloch-Grüneisen theorem

Abstract: We have measured the resistances (and resistivities) of Ag and Cu nanowires of diameters ranging from $15\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the temperature range $4.2--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with the specific aim of assessing the applicability of the Bloch-Gr\"uneisen formula for electron-phonon resistivity in these nanowires. The wires were grown within polymeric templates by electrodeposition. We find that in all the samples the resistance reaches a residual value at $T=4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the temperature dependence of resistance can be fitted to the Bloch-Gr\"uneisen formula in the entire temperature range with a well-defined transport Debye temperature $({\ensuremath{\Theta}}_{R})$. The values of the Debye temperature obtained from the fits lie within 8% of the bulk value for Ag wires of diameter $15\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ while for Cu nanowires of the same diameter the Debye temperature is significantly less than the bulk value. The electron-phonon coupling constants (measured by ${\ensuremath{\alpha}}_{\mathit{el}\text{\ensuremath{-}}\mathit{ph}}$ or ${\ensuremath{\alpha}}_{R}$) in the nanowires were found to have the same value as in the bulk. The resistivities of the wires were seen to increase as the wire diameter was decreased. This increase in the resistivity of the wires may be attributed to surface scattering of conduction electrons. The specularity $p$ was estimated to be about 0.5. The observed results allow us to obtain the resistivities exactly from the resistance and give us a method of obtaining the exact numbers of wires within the measured array (grown within the template).

A survey of temporal data mining

Abstract: Data mining is concerned with analysing large volumes of (often unstructured) data to automatically discover interesting regularities or relationships which in turn lead to better understanding of the underlying processes. The field of temporal data mining is concerned with such analysis in the case of ordered data streams with temporal interdependencies. Over the last decade many interesting techniques of temporal data mining were proposed and shown to be useful in many applications. Since temporal data mining brings together techniques from different fields such as statistics, machine learning and databases, the literature is scattered among many different sources. In this article, we present an overview of techniques of temporal data mining. We mainly concentrate on algorithms for pattern discovery in sequential data streams. We also describe some recent results regarding statistical analysis of pattern discovery methods.

Single-symbol maximum likelihood decodable linear STBCs

Abstract: Space-time block codes (STBCs) from orthogonal designs (ODs) and coordinate interleaved orthogonal designs (CIOD) have been attracting wider attention due to their amenability for fast (single-symbol) maximum-likelihood (ML) decoding, and full-rate with full-rank over quasi-static fading channels. However, these codes are instances of single-symbol decodable codes and it is natural to ask, if there exist codes other than STBCs form ODs and CIODs that allow single-symbol decoding? In this paper, the above question is answered in the affirmative by characterizing all linear STBCs, that allow single-symbol ML decoding (not necessarily full-diversity) over quasi-static fading channels-calling them single-symbol decodable designs (SDD). The class SDD includes ODs and CIODs as proper subclasses. Further, among the SDD, a class of those that offer full-diversity, called Full-rank SDD (FSDD) are characterized and classified. We then concentrate on square designs and derive the maximal rate for square FSDDs using a constructional proof. It follows that 1) except for N=2, square complex ODs are not maximal rate and 2) a rate one square FSDD exist only for two and four transmit antennas. For nonsquare designs, generalized coordinate-interleaved orthogonal designs (a superset of CIODs) are presented and analyzed. Finally, for rapid-fading channels an equivalent matrix channel representation is developed, which allows the results of quasi-static fading channels to be applied to rapid-fading channels. Using this representation we show that for rapid-fading channels the rate of single-symbol decodable STBCs are independent of the number of transmit antennas and inversely proportional to the block-length of the code. Significantly, the CIOD for two transmit antennas is the only STBC that is single-symbol decodable over both quasi-static and rapid-fading channels.

Testing metabolic ecology theory for allometric scaling of tree size, growth and mortality in tropical forests

Abstract: The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 oldgrowth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory’s predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.

Novel Photocatalysts for the Decomposition of Organic Dyes Based on Metal-Organic Framework Compounds

Abstract: Three novel metal-organic frameworks (MOFs) [Co2(C10H8N2)][C12H8O(COO)2]2, 1, [Ni2(C10H8N2)2][C12H8O(COO)2]2·H2O, 2, and [Zn2(C10H8N2)][C12H8O(COO)2]2, 3, with three-dimensional structures have been synthesized and characterized. The structures of the three compounds appear somewhat related, formed by the connectivity involving the metal polyhedra (Co4N trigonal bipyramids in 1, NiO4N2 octahedra in 2, and ZnO4 tetrahedra and ZnO3N2 trigonal bipyramids in 3), 4,4‘-oxybis(benzoate), and 4,4‘-bipyridine. The photocatalytic studies on 1−3 indicate that they are active catalysts for the degradation of orange G, rhodamine B, Remazol Brilliant Blue R and methylene blue. The compounds have also been characterized by powder X-ray diffraction, IR, thermogravitmetric analysis, UV−vis, photoluminescence, and magnetic studies.

A literature review, classification and simple meta-analysis on scheduling of batch processors in semiconductor

Abstract: In this paper, we present a literature review, classification schemes and a simple meta-analysis for scheduling of batch processors (SBP) research in semiconductor manufacturing (SM). This review is based on a study of journals and web-based documents/articles, which include conference materials, lecture notes in computer science, working papers, etc. There are 98 articles published in various publication outlets between 1986 and October 2004. Based on the literature review carried out and the nature of SBP research observed in SM, we have introduced two classification schemes to systematically organize the published articles. The first classification scheme is based on the problem configurations of SBP research in SM and the second one is based on the solution methodology followed by the researchers. These classification schemes indicate that there is much research scope on SBP research in SM. Furthermore, a simple meta-analysis is carried out to enhance understanding on the development and evolution of SBP research in SM and to identify potential research areas for further research and for improvement. The results show that there is an increasing trend in SBP research in SM. A comprehensive list of references is presented. This study is expected to provide a source of reference for other researchers (or readers), who are interested in SBP research particularly in SM and help stimulate further interest.

Explicit Space–Time Codes Achieving the Diversity–Multiplexing Gain Tradeoff

Abstract: A recent result of Zheng and Tse states that over a quasi-static channel, there exists a fundamental tradeoff, referred to as the diversity-multiplexing gain (D-MG) tradeoff, between the spatial multiplexing gain and the diversity gain that can be simultaneously achieved by a space-time (ST) code. This tradeoff is precisely known in the case of independent and identically distributed (i.i.d.) Rayleigh fading, for Tgesnt+nr-1 where T is the number of time slots over which coding takes place and nt,nr are the number of transmit and receive antennas, respectively. For T nt case, we present two general techniques for building D-MG-optimal rectangular ST codes from their square counterparts. A byproduct of our results establishes that the D-MG tradeoff for all Tgesnt is the same as that previously known to hold for Tgesnt+n r-1

MnO and NiO nanoparticles: synthesis and magnetic properties

Abstract: Nanoparticles of MnO with average diameters in the 6–14 nm range have been prepared by the decomposition of manganese cupferronate in the presence of TOPO, under solvothermal conditions. Nanoparticles of NiO with average diameters in the 3–24 nm range have been prepared by the decomposition of nickel cupferronate or acetate under solvothermal conditions. The nanoparticles have been characterized by X-ray diffraction and transmission electron microscopy. Both MnO and NiO nanoparticles exhibit supermagnetism, accompanied by magnetic hysteresis below the blocking temperature (TB). The TB increases with the increase in particle size in the case of NiO, and exhibits the reverse trend in the case of MnO.

Cytosolic Triacylglycerol Biosynthetic Pathway in Oilseeds. Molecular Cloning and Expression of Peanut Cytosolic Diacylglycerol Acyltransferase

Abstract: Triacylglycerols (TAGs) are the most important storage form of energy for eukaryotic cells. TAG biosynthetic activity was identified in the cytosolic fraction of developing peanut (Arachis hypogaea) cotyledons. This activity was NaF insensitive and acyl-coenzyme A (CoA) dependent. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the final step in TAG biosynthesis that acylates diacylglycerol to TAG. Soluble DGAT was identified from immature peanuts and purified by conventional column chromatographic procedures. The enzyme has a molecular mass of 41 ± 1.0 kD. Based on the partial peptide sequence, a degenerate probe was used to obtain the full-length cDNA. The isolated gene shared less than 10% identity with the previously identified DGAT1 and 2 families, but has 13% identity with the bacterial bifunctional wax ester/DGAT. To differentiate the unrelated families, we designate the peanut gene as AhDGAT. Expression of peanut cDNA in Escherichia coli resulted in the formation of labeled TAG and wax ester from [14C]acetate. The recombinant E. coli showed high levels of DGAT activity but no wax ester synthase activity. TAGs were localized in transformed cells with Nile blue A and oil red O staining. The recombinant and native DGAT was specific for 1,2-diacylglycerol and did not utilize hexadecanol, glycerol-3-phosphate, monoacylglycerol, lysophosphatidic acid, and lysophosphatidylcholine. Oleoyl-CoA was the preferred acyl donor as compared to palmitoyl- and stearoyl-CoAs. These data suggest that the cytosol is one of the sites for TAG biosynthesis in oilseeds. The identified pathway may present opportunities of bioengineering oil-yielding plants for increased oil production.

Defining the ‘modified Griffin plot’ in vortex-induced vibration: revealing the effect of Reynolds number using controlled damping

Abstract: In the present work, we study the transverse vortex-induced vibrations of an elastically mounted rigid cylinder in a fluid flow. We employ a technique to accurately control the structural damping, enabling the system to take on both negative and positive damping. This permits a systematic study of the effects of system mass and damping on the peak vibration response. Previous experiments over the last 30 years indicate a large scatter in peak-amplitude data ($A^*$) versus the product of mass–damping ($\alpha$), in the so-called ‘Griffin plot’.

A brief review of the status, distribution and biology of wild Asian elephants Elephas maximus

Abstract: The Asian elephant Elephas maximus is distributed discontinuously across the Asian continent. The total wild population is 38 500-52 500, with a further c. 16 000 in captivity, the majority of which are in range countries. India has 60% of the global population of wild Asian elephants. The species has a multi-tiered social system with ♀♀ living in matriarchal groups of five to 20 individuals that interact with other family units in the area. Adult ♂♂ live alone or in small, temporary groups with weak social bonds. Asian elephants are megaherbivores that spend 12-18 hours per day feeding, and they eat browse and plants depending on availability and season. Home-range size is dependant on the availability of food, water and shelter in the region. Loss and fragmentation of habitat, human-elephant conflicts and poaching are the greatest threats to the species. Asian elephants are managed using traditional and modern methods but progress still needs to be made to improve welfare, training and breeding for these animals.

Survival Signaling by Notch1: Mammalian Target of Rapamycin (mTOR)–Dependent Inhibition of p53

Abstract: Notch signaling is believed to promote cell survival in general. However, the mechanism is not clearly understood. Here, we show that cells expressing intracellular domain of human Notch1 (NIC-1) are chemoresistant in a wild-type p53-dependent manner. NIC-1 inhibited p53 by inhibiting its activating phosphorylations at Ser(15), Ser(20), and Ser(392) as well as nuclear localization. In addition, we found that inhibition of p53 by NIC-1 mainly occurs through mammalian target of rapamycin (mTOR) using phosphatidylinositol 3-kinase (PI3K)-Akt/protein kinase B (PKB) pathway as the mTOR inhibitor, rapamycin treatment abrogated NIC-1 inhibition of p53 and reversed the chemoresistance. Consistent with this, rapamycin failed to reverse NIC-1-induced chemoresistance in cells expressing rapamycin-resistant mTOR. Further, ectopic expression of eukaryotic initiation factor 4E (eIF4E), a translational regulator that acts downstream of mTOR, inhibited p53-induced apoptosis and conferred protection against p53-mediated cytotoxicity to similar extent as that of NIC-1 overexpression but was not reversed by rapamycin, which indicates that eIF4E is the major target of mTOR in Notch1-mediated survival signaling. Finally, we show that MCF7 (breast cancer) and MOLT4 (T-cell acute lymphoblastic leukemia) cells having aberrant Notch1 signaling are chemoresistant, which can be reversed by both PI3K and mTOR inhibitors. These results establish that Notch1 signaling confers chemoresistance by inhibiting p53 pathway through mTOR-dependent PI3K-Akt/PKB pathway and imply that p53 status perhaps is an important determinant in combination therapeutic strategies, which use mTOR inhibitors and chemotherapy.

The importance of demographic niches to tree diversity.

Abstract: Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.

Supersymmetry parameter analysis : SPA convention and project

Abstract: High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e(+)e(-) linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

Surface freshwater from Bay of Bengal runoff and Indonesian Throughflow in the tropical Indian Ocean

Abstract: According to recent estimates, the annual total continental runoff into the Bay of Bengal (BoB) is about 2950 km 3, which is more than half that into the entire tropical Indian Ocean (IO). Here we use climatological observations to trace the seasonal pathways of near surface freshwater from BoB runoff and Indonesian Throughflow (ITF) by removing the net contribution from precipitation minus evaporation. North of 20 degrees S, the amount of freshwater from BoB runoff and ITF changes with season in a manner consistent with surface currents from drifters. BoB runoff reaches remote regions of the Arabian Sea; it also crosses the equator in the east to join the ITF. This freshwater subsequently flows west across the southern tropical IO in the South Equatorial Current.

Optimal Reservoir Operation Using Multi-Objective Evolutionary Algorithm

Abstract: This paper presents a Multi-objective Evolutionary Algorithm (MOEA) to derive a set of optimal operation policies for a multipurpose reservoir system. One of the main goals in multi-objective optimization is to find a set of well distributed optimal solutions along the Pareto front. Classical optimization methods often fail in attaining a good Pareto front. To overcome the drawbacks faced by the classical methods for Multi-objective Optimization Problems (MOOP), this study employs a population based search evolutionary algorithm namely Multi-objective Genetic Algorithm (MOGA) to generate a Pareto optimal set. The MOGA approach is applied to a realistic reservoir system, namely Bhadra Reservoir system, in India. The reservoir serves multiple purposes irrigation, hydropower generation and downstream water quality requirements. The results obtained using the proposed evolutionary algorithm is able to offer many alternative policies for the reservoir operator, giving flexibility to choose the best out of them. This study demonstrates the usefulness of MOGA for a real life multi-objective optimization problem.

Design and performance evaluation of subsynchronous damping controller with STATCOM

Abstract: A long transmission line needs controllable series as well as shunt compensation for power flow control and voltage regulation. This can be achieved by suitable combination of passive elements and active FACTS controllers. In this paper, series passive compensation and shunt active compensation provided by a static synchronous compensator (STATCOM) connected at the electrical center of the transmission line are considered. It is possible to damp subsynchronous resonance (SSR) caused by series capacitors with the help of an auxiliary subsynchronous damping controller (SSDC) on STATCOM. The objective of this paper is to investigate the SSR characteristics of the system and propose a new design procedure for SSDC based on nonlinear optimization to meet the specifications on the damping torque in the range of critical torsional frequencies. The SSDC uses the Thevenin voltage signal to modulate the reactive current reference of STATCOM. The Thevenin voltage signal is derived from the locally available STATCOM bus voltage and reactive current signals. The STATCOM configurations considered in this paper are 12 pulse, two- and three-level voltage source converter with Type-2 and Type-1 control, respectively. The controller regulates either reactive current (supplied by the STATCOM) or the bus voltage. The 3-phase model of the STATCOM is based on switching functions. By neglecting harmonics in the switching function, D-Q model is derived which is combined with similar models of the other system components for linear analysis. The results of the linear analysis are validated by carrying out transient simulation based on the detailed nonlinear models. The study is performed on the system adapted from the IEEE First Benchmark Model.

Two internal ribosome entry sites mediate the translation of p53 isoforms

Abstract: The p53 tumour suppressor protein has a crucial role in cell-cycle arrest and apoptosis. Previous reports show that the p53 messenger RNA is translated to produce an amino-terminal-deleted isoform (ΔN-p53) from an internal initiation codon, which acts as a dominant-negative inhibitor of full-length p53. Here, we show that two internal ribosome entry sites (IRESs) mediate the translation of both full-length and ΔN-p53 isoforms. The IRES directing the translation of full-length p53 is in the 5′-untranslated region of the mRNA, whereas the IRES mediating the translation of ΔN-p53 extends into the protein-coding region. The two IRESs show distinct cell-cycle phase-dependent activity, with the IRES for full-length p53 being active at the G2–M transition and the IRES for ΔN-p53 showing highest activity at the G1–S transition. These results indicate a novel translational control of p53 gene expression and activity.